There has been known hollow silica particles each having the diameter in the range from about 1 to about 300 μm (Refer to, for instance, Patent Document 1 and Patent Document 2). Further there has been known a method of producing hollow particles each comprising a fine silica shell by depositing active silica from an aqueous solution of alkali silicate metal on a core made from a material other than silica and removing the material without breaking the silica shell (Refer to Patent Document 3 and other related documents).
This applicant previously proposed to obtain composite oxide particles with a nanometer size and a low refractive index by completely coating a surface of a porous inorganic oxide particle with silica or the like (Refer to Patent Document 5), and also proposed to obtain hollow silica-based particles each with a nanometer size and a low refractive index by forming a silica coating layer on core particles of a composite oxide each comprising silica and an inorganic oxide other than silica and removing the inorganic oxide other than silica to coat the particle with silica according to the necessity (Refer to Patent Document 6).
Each of the types of particles described above has a low refractive index, and the particles are used for blending in a reflection reducing coating for various types of display units, and to produce excellent transparency of the reflection reducing coating or to reduce haze therein, generally particles each with the diameter of about 0.2 μm or below are used. Further, also the porous particles have the capability of reducing reflection, so that the porous particles are used to form a reflection reducing coating for a display unit.
On the other hand, electronic equipment such as a display device has a problem of deposition of foreign particles or dusts caused on electrification, and further negative effects by electromagnetic waves emitted from electronic equipment over human health are other problems of growing concerns. To overcome this problem, recently an antistatic coating, an electromagnetic masking film or the like with a conductive material blended therein is provided on a surface of a display device or the like, and in this case, particles of metals such as silver or silver-palladium or those of oxides such as tin-doped indium oxide, or antimony-doped tin oxide are used as the conductive materials. However, the conductive particles as described above have a high refractive index respectively and further the metallic particles are colored, so that there are various restrictions not only in the blending rate, particle diameter, dispersibility, but also in the economical aspect.    [Patent Document 1] Japanese Patent Laid-Open Publication No. HEI 6-330606    [Patent Document 2] Japanese Patent Laid-Open Publication No. HEI 7-013137    [Patent Document 3] Japanese Patent Laid-Open Publication No. 2000-500113    [Patent Document 4] Japanese Patent Laid-Open Publication No. HEI 11-029318    [Patent Document 5] Japanese Patent Laid-Open Publication No. HEI 7-133105    [Patent Document 6] Japanese Patent Laid-Open Publication No. 2001-233611